The present invention is directed to the implantation of artificial joint components and in particular to acetabular joint components. More particularly, it is related to instrumentation for reaming the acetabular socket and for locating the prosthetic acetabular cup within the reamed socket. Even more particularly, it is related to an instrument which can be used with computer-assisted minimally invasive surgical implantation of the joint component during joint replacement or revision procedures.
Total hip replacement or orthroplasty operations have been performed to repair the acetabulum and the regions surrounding it and to replace the hip components such as the natural femoral head which has degenerated.
With regard to the acetabulum, many instruments have been designed to locate either the acetabular cup or reamers for repairing the acetabulum to receive such a prosthetic cup. Such instruments are shown in U.S. Pat. Nos. 4,305,394, 4,632,111, 5,037,424, 5,061,270, 5,320,625 and 6,395,005. Many of these instruments require a relatively large incision, i.e., 7–9 inches in the hip area in order to utilize the instruments in preparing the acetabulum and positioning the acetabular cup. There has been a long felt need to develop instrumentation to perform this procedure which can be used with a smaller incision, for example, 2–3 inches.
In addition, computer-assisted surgery has been developed which utilizes a tracking system which can relate positions on the patients and/or instruments to stored X-ray, CT scan and MRI data previously obtained for the patient. Alternately, image free computer-aided surgery has been developed where mechanical relationships can be calculated from anatomical reference points and utilized such as in joint arthroplasty. Such digitized points include the location of the center of the femoral head, the location of the epicondylar ligament attachment points, and the surfaces of the condyles. These systems are used intra-operatively for performing various surgical procedures, including replacement of artificial joints.
It has been especially useful to utilize trackable medical instruments for use in procedures utilizing computer-assisted image guided or image free medical and surgical navigation systems. Systems using body images are shown in U.S. Pat. No. 5,383,454 to Bucholz and U.S. Pat. No. 6,021,343 to Foley et al. In general, these image-guided systems use computer stored digital images of a body part obtained, such as by CT scans taken before surgery, to generate images on a display, such as a CRT monitor screen, during surgery. These images are used in connection with real time information for representing the position of a surgical instrument with respect to the body part. The systems typically include tracking devices such as, for example, an LED array mounted on a surgical instrument as well as a patient body part or parts. A tracker such as an optical tracker is used to track, in real time, the position of the body part and the instrument used during surgery, and a monitor screen to display images representing the body and the position of the instrument relative to the stored images or a vertical image as the surgical procedure is performed.
An image free type system is shown in U.S. Pat. No. 6,385,475 the teachings of which are incorporated herein by reference. Some systems of this type include virtual joint images and relate the tracked anatomic landmarks to the virtual body part images. In such a system, an active or passive marker is attached to bones on opposite sides of a joint and a measuring device such as an optical sensing camera is coupled to a data processing system to which signals corresponding to the positioning data of the optical markers are supplied by the optical camera system. This data is used to correlate the markers on opposite sides of the joint with digitized anatomic landmarks. With a pointer mounted tracker, it is possible to locate various anatomic reference points on the joints to allow the optical/computer system to position a cutting instrument such as a reamer or sawblade having a tracker mounted thereon to shape a joint part for receiving a prosthetic implant.
In utilizing instruments which rotate such as reaming systems, it is important to align the cutting tool in the correct angle as well as locating and controlling the depth of penetration. There has been a long felt need for a tool which can axially align a reamer such as an acetabular reamer and guide the reamer internally of the body to a precise desired location. In addition, in order to perform minimally invasive surgery, reamers have been designed for the acetabulum which, rather than having the standard hemispherical shape, have only a part hemispherical shape but must be rotated through an angle such as 180° to form the hemispherical surface of an acetabular cavity in the pelvis designed to receive a hemispherical prosthetic acetabular component. An expandable reamer such as shown in U.S. Pat. No. 3,702,611 may be used.